#include <iostream>
#include <fstream>

using namespace std;

ifstream f("ciur.in");
ofstream g("ciur.out");

int n, s;
bool v[2000001];

int main()
{
    cin >> n;

    for ( int i = 2; i * i<= n; i += 1)
        for ( int j = 2; j * i <= n; j += 1 )
            v[i*j] = 1;
    for ( int i = 2; i <= n; i++)
        if( v[i] == 0)
        s++;
    cout << s;
    f.close();
    g.close();
    return 0;
}